Vintage analog medical telemetry from the 1970s exhibited a typical maximum data loss of 50 minutes per day, an enormous improvement over no patient monitoring. The initial digital systems stumbled as they exhibited 75 minutes per day of lost data. Over time improvements were made but second generation UHF telemetry still exhibited 25 minutes of dropout per day. This included most systems running in the Wireless Medical Telemetry Service (WMTS).
The medical world received a wakeup call when a High Definition Television (HDTV) station test near Baylor Hospital impacted patient telemetry. If a digital television station transmits in the same channel as UHF telemetry, virtually no data are transmitted successfully, which is why the Food and Drug Administration (FDA) and Association for the Advancement of Medical Instrumentation (AAMI) petitioned the Federal Communications Commission (FCC) for a band dedicated to medical telemetry, resulting in the WMTS. This allocation precludes a television station using the dedicated band, but does not result in any improvement over the 25 minutes per day of dropout.
Some companies have improved on second generation digital by copying the 802.11 Access Point (AP) concept, including using spread spectrum technology. As with any spread spectrum technology, the high ratio of available bandwidth to data bandwidth is important. With only 6 MHz available, these proprietary systems prefer to use the full 608-614 MHz band and therefore other medical telemetry systems are essentially rendered useless when operated nearby. Other WMTS solutions include re-crystalling existing systems. While this expensive “upgrade” removes the worry of an in-band HDTV station, it does nothing to improve the 25 minutes per day of dropout.
About the same time as WMTS was being considered in 1999, IEEE 802.11 was ratified and some medical device companies embraced the concept of standards-based solutions as a means to make better use of networks by sharing one network among many applications. At that time, the promise was unrealized because standards and protocols for security and quality of service had not yet been developed. Even so, using 802.11 for medical telemetry brought a 10-fold decrease in dropout [S. D. Baker, et al., “Performance Measure of ISM-Band and Conventional Telemetry,” IEEE EMB, vol. 23, pp. 27-36m, May/June 2004] that is realized because of a robust modulation, intelligent communication protocols, and good radio frequency (RF) network design.
Since then, wireless Local Area Networks (LANs) have become ubiquitous in many industries and even within the cautious healthcare environment: nearly 50 percent of hospitals have 802.11 LANs installed and over 80 percent are planning to have an 802.11 network deployed to support Electronic Medical Records (EMR) within the next two years.